In July and August of 2013, the Oregon State University Plant Clinic received 2-year-old ‘Draper’ and ‘Duke’ blueberry plants (Vaccinium corymbosum L.) from Yakima County, WA, with cambial discoloration and cane dieback in the absence of girdling cankers. Surface-disinfected diseased tissue was aseptically transferred to streptomycin potato dextrose agar (SPDA) and incubated at 20°C. A fungus with initially white, then pale to dark gray aerial mycelium was consistently recovered. The fungus grew rapidly on SPDA, and produced pycnidia after 4 to 7 days of incubation at 23°C, under a 12/12 h near-UV light. Pycnidia were unilocular and dark brown. Conidia were initially hyaline, granular, aseptate, subcylindrical to elliptical, thick-walled, then becoming one septate and dark brown with age, measuring 25.6 to 32.5 × 15.2 to 18.4 μm (avg. 30.2 × 16.8 μm, n = 40), with longitudinal striations, and a length to width ratio of 1.76 to 1.84 (avg. 1.80). Morphological characteristics were consistent with the genus Lasiodiplodia (†). DNA was extracted from the mycelium of four single-spore isolates collected from three locations in eastern Washington. A Bayesian phylogenetic analysis was performed with 59 contigs representing 26 Lasiodiplodia spp. using partial sequences from the internal transcribed spacer (ITS) region using primers ITS1/ITS4, and the elongation factor 1-alpha (EF1-α) region from primers EF526F/EF1567R (664 characters). Our isolates formed a well-supported monophyletic clade with L. mediterranea ex-type sequences. On the basis of overlapping morphological traits and a multilocus phylogenetic analysis, the fungus was identified as L. mediterranea Linaldeddu, Deidda & Berraf-Tebbal (†). Sequence data from three of the isolates were deposited into GenBank (ITS: KU578250–52; EF: KU720485–87; β-tubulin: KU720482–84). To fulfill Koch’s postulates, ten 1-year-old plants each of ‘Duke’ and ‘Draper’ were inoculated by placing 3-day-old, colonized, 4 mm SPDA plugs onto stem wounds created by lightly shaving the bark with a sterile scalpel. Five control plants were inoculated with noncolonized plugs. All wounds were covered with Parafilm. After 2 to 4 weeks, inoculated plants displayed cambial discoloration, lesion formation around inoculation sites, and some cane dieback. Control plants remained symptomless. L. mediterranea was consistently recovered from the lesion margins of inoculated plants. Isolates were identified morphologically and by sequencing, as above. An additional replicate yielded identical results. L. mediterranea has been reported from Italy and Algeria, on trunks and branches of Vitis vinifera, Quercus ilex, and Citrus × sinensis (†). Several other Botryosphaeria-type fungi have been associated with blueberry cane dieback and have been reported from New Jersey (U.S.A.), Chile, China, Mexico, and New Zealand (†). However, to our knowledge, this is the first report of L. mediterranea causing stem lesions and dieback on blueberry. Nearly 3% of second leaf blueberries died in the affected locations. Washington is the 4th largest producer of U.S. blueberries and production has expanded in recent years; given that this disease can cause dieback of stems, it has the potential to significantly reduce the life of productive fields. © 2017, American Phytopathological Society. All rights reserved.
